Seat Cutter - Valve Spring - M8Machine valve spring seats for proper installed spring height and spring cup fitment Hardened pilots fit all 3 8" and 1 2" hand drills Cutter bodies and pilots are interchangeable Cutter: Cuts spring seat 0. 550" ID x 1. 180" OD The M8 cylinder head material under the valve spring seat pocket to the top side of the exhaust port is fairly thin even more so on ported cylinder heads. Designed for M8 cylinder heads using high lift camshafts see Feuling M8